In processing of such silicon wafers and the like the wafers are subjected to numerous process steps involving highly active liquid chemicals such acids and rinsing water, and gases which are generally used in drying the wafers between other process steps. Such liquids and gases are often applied by spraying onto the wafers in such centrifugal spray processing. The wafers are revolved in a closed processing chamber.
Processing machines defining such a process chamber are typically arranged with a wafer carrying rotor revolving on an upright axis, substantially as illustrated in U.S. Pat. Nos. 4,132,567 and 3,990,462. The housing defining the process chamber provides a drain in the bottom of the housing through which liquids and some gases are drained or evacuated from the chamber.
In other processing machines, the wafer carrying rotor may be arranged to revolve on a generally horizontal axis or on an axis inclined by a few degrees above the horizontal. In such a machine, as illustrated in U.S. Pat. No. 4,300,581, the liquid drainage and discharge of the gases occurs at the lower side of the generally cylindrical wall of the housing defining the process chamber. In that patent, the lowermost portion of the cylindrical peripheral wall simply has a slot extending parallel to the axis, and a drainage collector at the outside of the housing connects to a drain pipe for discharging the liquids and gases.
It has been found that the removal of all of the droplets of liquid from the walls of the processing chamber is difficult to accomplish with the equipment known previously. The droplets of rinsing water often remain on the peripheral wall of the chamber and on the inside face of the door, on the drying cycle in the processing machine is continued so long as to evaporate the liquid droplets. Previously, doors have incorporated a heating devices ask to vaporize liquid droplets which may collect thereon, but the use of such heating devices in the door is not practical in such doors that may incorporate a transparent panel.